Effects of the Addition of Poly(ethylene Glycol) and Non-ionic Surfactants on Pretreatment, Enzymatic Hydrolysis, and Ethanol Fermentation

The consolidation of cellulosic ethanol on the market is fundamental to mitigate the consumption of fuels from fossil sources and to reduce the impact caused by the large generation of agro-industrial waste. In order to achieve this objective, some challenges of cellulosic ethanol technology must be overcome, including the improvement of the cellulosic ethanol production steps. Several studies propose the use of poly(ethylene glycol) (PEG) and non-ionic surfactants (such as Tween 80, Tween 20, and Triton X-100) as a way to increase cellulosic ethanol titers. The benefits attributed to the PEG and non-ionic surfactants go beyond the increase of the concentration of free cellulases during enzymatic hydrolysis. Successful cases of pretreatments of lignocellulosic biomasses assisted by PEG and surfactants and the detoxification of inhibitor-rich hydrolysates with PEG reveal the existence of a plethora of positive mechanisms. Therefore, the present review article is focused on the benefits and mechanisms involved in the addition of PEG and non-ionic surfactants in the pretreatment, enzymatic hydrolysis, and ethanol fermentation steps. Interactions between additives and lignin as well as schemes based on high PEG concentrations were also discussed in detail.